1. Field of the Invention
The present invention relates in general to apparatus and method for disposal of putrescent waste material and in particular the continuous bio-conversion of putrescent waste material.
2. Description of Related Art
The production of organic compost for municipal refuse or garbage is well known. For example, U.S. Pat. No. 5,082,486 filed on Nov. 16, 1990 by Glogowski teaches a method for the production of organic compost comprising the following steps:
1. shredding the refuse;
2. adding water to saturation;
3. adding earthworms;
4. keeping the water content at more than 80% during at least 30 days; and
5. keeping the mixture at a temperature from 0-54xc2x0 C. and with a moisture of at least 45% during more than 4 months.
Such a method is not suitable for continuous treatment of large amounts of putrescent waste. Furthermore, the separation of earthworms from the treated waste materials is very difficult.
The prior art suggests various types of bio-conversion facilities for facilitating the production of useful animal products from putrescent waste material. One device and associated method relates to the continuous treatment of large amounts of humid putrescent waste materials by means of fly larvae. Thus, after a relatively short period of a few days, the putrescent waste is converted into a slightly moist odor-free compost. After treatment of the waste materials, the use of fly larvae allows for separation of the larvae from the waste. Live or dehydrated larvae constitute an excellent feed stock for fish and poultry, but the larvae can also be used for the production of by-products such as protein meal, chitin, and chitosan. It has been observed that when using fly larvae for the treatment of putrescent waste materials, it is possible to induce them to crawl out of the waste by exposing the waste to an illumination, preferably together with a heating, especially an infrared illumination, whereby the separation of the larvae out of the putrescent waste is obtained by the larvae themselves.
FIG. 1 is a flow diagram of a prior art bio-conversion facility for continuous treatment of putrescent waste by means of fly larvae in which the fly larvae actually eat the waste. Facility 100 is further described by U.S. Pat. No. 5,759,224 filed on Aug. 22, 1996 by Paul A. Oliver and is incorporated by reference herein in its entirety. Facility 100 comprises walls 101 defining fly larvae cultivation chamber 102 for the treatment of putrescent waste. A stack of at least two conveyor belt systems 108, each having a waste reception zone 108A, a treatment zone 108B in which the putrescent waste is more or less completely eaten by fly larvae, and an evacuation zone 108C, is designed so as to transport the waste and the fly larvae eating the waste from the reception zone 108A towards the evacuation zone 108C. A system 130 grinds putrescent waste material to be treated so as to form a pulp containing particles of more or less uniform grain size, the grain size being preferably smaller than the size of the mature fly larvae mouth, and a blending and holding tank 140 contains the ground putrescent waste. Pump 148 transfers the waste from the blending and holding tank 140 to paddle box 131. Variable speed control system 149 for pump 148 controls the discharge rate of waste into paddle box 131. A pipe or other transfer means 150 is used to transfer the ground waste from pump 148 into paddle box 131, the pipe or transfer means 150 being provided with heating system 144.
Valve 151 is mounted on pipe 150 to select sequentially the specific paddle box 131 and conveyor belt 108 that are to receive the waste. The distribution paddle box 131 has paddles that, in the preferred embodiment, turn in a direction opposite the flow of material so as to ensure a more or less even deposition of the ground putrescent waste down an inclined chute onto the central section of a long conveyor belt (80-100 meters), leaving the lateral surfaces of the conveyor belt free of waste. One or more distribution bags 110 contain an aqueous suspension of fly larvae eggs, the bags 110 being made preferably of plastic, and being connected to one or more tubes 145 through which the suspension liquid containing eggs drops onto the waste exiting the paddle box. A container with holes in the bottom could also be used to drip larvae onto the conveyor belt 108. A motor and speed reducer drives the conveyor belt 108, the motor being associated with a system well known in the art for controlling the speed of the conveyor belt 108. An air-conditioning system 112 controls the most appropriate temperature, humidity, and oxygen content in the fly larvae cultivation chamber (for example, between 28xc2x0 C.-38xc2x0 C. [82xc2x0 F.-100xc2x0 F.] between 30-90% relative humidity), depending on the species of fly larvae used. An air-scrubbing system 113 deodorizes the waste material leaving the fly larvae cultivation chamber in a well-known manner.
Infrared lamps 115 are located in evacuation zone 108C for inducing the larvae to crawl out of the waste. Two troughs 116, one on each lateral side of the conveyor belt (not shown), collect and transport the larvae falling or sliding from conveyor belt 108, each trough 116 having a water inlet (inlet 117) so as to create a high-speed water stream for transporting the larvae out of the trough, as well as an outlet (outlet 147) for evacuating the water and fly larvae. Transfer pipe 146 connects outlet 147 of a first conveyor belt trough to inlet 117 of a second conveyor belt trough, the second conveyor belt preferably being situated below the first. Pipe 118 through which the water stream with larvae flows toward a central rinsing and de-watering device 119 that may be, for example, a vibratory de-watering screen. Conveyor belt scraper 141 is used for scraping and cleaning the conveyor belt and for transferring the fly larvae residue onto chute 142. Centralized conveyor belt 143 receives waste from one or more waste chutes 142 and a storage area or surge bin (not shown) receives the waste from conveyor belt 143. Variable speed control system 123 is used to determine the speed or the intermittent movement of the conveyor belt (for example, if the larvae in the evacuation zone have not reached optimal maturation, the speed of the conveyor belt is reduced so as to increase the residence time of the larvae on the conveyor belt). System 132, shown in phantom lines in FIG. 1 and well known in the art, may be used for measuring the thickness of the waste deposited on the conveyor belt and controlling the amount of eggs or larvae to be added to the waste, so that the appropriate amount of eggs or larvae is added according to the thickness of waste on the belt, the system controlling, for example, the outlet of eggs or larvae from the distribution box 110. System 138, well known in the art, can be used for determining the presence of heavy metals or other contaminants in the waste, the system preventing the entry of contaminated waste into the blending and holding tank 140.
Paddle box 131 ensures an even deposition of the waste from a chute incorporated in paddle box 131, between distribution arms, on conveyor belt 108, but not over the entire width of the conveyor belt 108. This leaves the lateral surfaces of conveyor belt 108 adjacent the lateral edges free of waste. The lateral surfaces are preferably about 10 cm in width and are provided with pins, needles, bristles, indentations, or holes, all of which may serve as a means for improving the detachment of waste particles adhering to the larvae crawling off the conveyor belt.
Upon reaching maturity, fly larvae naturally crawl out of the waste but, since they do not all reach maturity at exactly the same time, infrared lamps 115 are used for inducing the fly larvae to crawl out of the waste and off the conveyor belt in a synchronized and orderly manner. Even the direction in which the fly larvae crawl can be controlled by means of the graduated application of light and heat. Lamps 115 are preferably mounted in the form of a triangle, with one corner of the triangle intersecting the vertical plane passing through the middle line of the conveyor belt as shown so as to induce the fly larvae to crawl left and right of the middle line. When the conveyor belt is in motion, preferably all the lamps within the triangle are ON. When the conveyor belt is not in motion, preferably only some of the lamps are ON, effectively providing a barrier across which the fly larvae would be reluctant to crawl. Instead the mature fly larvae move laterally on conveyor belt 108 into one of the two troughs 116 on each lateral side of conveyor belt 108 for collection. The larvae collected in the trough 116 can be sold as live fly larvae, but preferably they are further treated in a plant 126 for producing protein meat, chitin, chitosan and other valuable products.
The above-described device and associated method discloses producing a continual supply of mature fly larvae by maintaining co-existing populations of fly larvae at different states of development. Putrescent waste materials and fly eggs are continually added to a conveyor belt on which fly larvae mature. Simultaneously, waste residue is continually scraped from the moving conveyor belt at a point on the conveyor after the fly larvae have matured. The waste residue may then be processed using an alternative bio-conversion process. Alternatively, the waste residue may be composted or sold as product. However, the above-described device is rather complex and expensive to construct, maintain and operate. Furthermore, in situ operations involving the invention are not cost effective because the putrescent waste material must be deposited on the conveyor belt in a specified position. This insures that the fly larvae extract the maximum nutritional value from the waste material prior to the waste residue being scraped from the conveyor belt.
FIG. 2 is a cutaway diagram of another prior art bio-conversion facility for treatment of putrescent waste The example described below has been developed by Craig Sheppard, Jeffery K. Tomberlin and Larry Newton at the National Environmentally Sound Production Laboratory at the College of Agriculture and Environmental Sciences at The University of Georgia. Facility 200 may also bio-convert putrescent waste by means of fly larvae whereby the fly larvae actually eat the waste material or bacteria which occurs on the waste, as discussed above with respect to facility 100 shown in FIG. 1. However, unlike facility 100, facility 200 depicted in FIG. 2 may be an in situ facility co-located with putrescent waste material producing operation.
Facility 200 depicts the bio-conversion of putrescent wastes from caged laying hens at an egg laying facility. Each laying hen excretes an amount of putrescent waste material and the fly larvae feed on the hen waste. Cages 244 are suspended in a staggered arrangement above disposal volume 202 in such a manner as to expose a maximum area of cage floor mesh to disposal area 202. By configuring cages 244 in such an arrangement, waste falls from cages 244 directly into disposal volume 202, thereby eliminating the need to transport the putrescent waste material to disposal volume 202. In the present arrangement, cages 244 are arranged in four separate stacks with walkways 242 on either side of each stack. Walkways 242 extend the length of facility 200, as do cages 244.
Positioned below walkways 242, disposal volume 202 is subdivided by wall 208. At either side of disposal area 202 ramps 204 are positioned which lead to collection tubes 206. Collection tubes 206 are fabricated with longitudinal openings adjacent to ramps 204 (not shown), which run the length of collection tubes 206. As the laying hens in cages 244 deposit putrescent waste into disposal area 202 fly eggs are introduced. Fly larvae hatch from the eggs. When the fly larvae mature, the mature larvae surface from the putrescent waste in search of a more favorable environment to pupate. Fly larvae feed in only the top few inches of waste, but interestingly a population of fly larvae will tend to self regulate its numbers in order to extract optimal nutrition from each layer of waste prior to reaching the maximum feeding depth of the fly larvae.
Once the fly larvae reach maturity, the mature larvae crawl out of the putrescent waste material and onto the surface. The fly larvae attempt to navigate off of the surface of disposal volume 202 and away from the waste, as the larvae no longer need to feed on the waste. Facility 200 affords the mature larvae with only one avenue of escape from the putrescent waste, up ramps 204 and into collection tubes 206 where the larvae are collected and processed.
The deposition of waste material and collection of mature fly larvae continue unabated until waste residue must be collected from disposal area 202. Waste residue is the byproduct of the putrescent waste material after the bio-conversion process. The waste residue is of no value to the fly larvae and therefore must be removed from beneath cages 244 in order to provide additional space for new putrescent waste. However, it is impossible to remove only the waste residue without also removing the colony of fly larvae feeding in the top layers of the putrescent waste. The waste residue may be removed manually with shovels or may instead be collected by the bucket of a front-end loader and transported from disposal volume 202.
While facility 200 has the advantage of being less complex and expensive to implement than bio-conversion facility 100 in FIG. 1 discussed above, it has a disadvantage of being less efficient than facility 100. With respect to facility 200, disposal area 202 contains a colony of fly larvae in different stages of development, from newly hatched larvae to mature larvae because new fly eggs are introduced to the waste as larvae leave the disposal area. The colony is homogeneously distributed across the top few inches of putrescent waste disposal volume 202. However, each time the waste residue is removed from disposal area 202 an entire colony of fly larvae is destroyed. Production of mature fly larvae can only resume after new fly eggs are laid and their larvae mature. Other inefficiencies inherent with facility 200 are due to the loss of the top few inches of putrescent waste before it can be fully converted by the fly larvae and problems associated with re-regulating the population of larvae with the rate of deposition from the laying hens.
The present invention relates in general to apparatus and method for disposal of putrescent waste material and in particular the continuous bio-conversion of putrescent waste material. Initially, putrescent waste is deposited on a surface of a disposal volume which is partially composed of putrescent waste. A living system bio-converts at least a portion of the putrescent waste in the disposal volume, transforming the putrescent waste into waste residue. While bio-conversion is occurring on a portion of the putrescent waste in the disposal volume, waste residue is excavated from the disposal volume below the surface of the disposal volume. Because the excavation takes place below the surface area, the bio-conversion process is not affected by excavating the waste residue. A device for continuous bio-conversion of putrescent waste comprises a disposal track having lateral side walls and floor for containing the disposal volume. An excavation gap is associated with at least one of the lateral side walls for excavating waste material from the disposal volume. The excavation gap is positioned substantially below the living system so waste can be excavated simultaneously with bio-conversion. The device further employs a scraper for excavating at least a portion of the waste residue. The scraper has a plurality of blades attached to a chain for excavating the waste and interposed between the blades are backplates which clean the blades as the chain rounds a sprocket. The scraper is moved along the floor of the disposal track as it excavates the waste material. The floor both supports the disposal volume and the scraper, and has a filter screen to filter water from the disposal volume.